Beyond a basal nutrient mixture of salts, sugars, amino acids, and vitamins, cells in vitro have also been found to require for proliferation a supplement of poorly defined biological fluids or extracts. Because of availability and ease of storage, the most commonly used supplement is serum.
The use of serum in cell culture media, however, has several disadvantages. Serum is comparatively expensive. Since serum is not a defined component, different lots of serum may vary in the concentration of compounds present and thus result in unpredictable culture growth. Serum may also be contaminated with viruses or mycoplasmas. The protein in serum may complicate the purification of cell products from the culture medium.
In efforts to overcome the disadvantages of serum containing medium, researchers have attempted to provide serum-free media by substituting defined or better characterized components for serum. Unfortunately, the complexity of serum and the differing growth requirements of different types of cells has made it difficult to provide such media. For reviews on serum-free media for insect cell culture see Mitsuhashi (1982) "Continuous Cultures of Insect Cell Lines in Media Free of Sera" Appl. Ent Zool. 17: 575-581; and Goodwin, "Growth of insect cells in serum-free media" in Techniques in the Life Sciences, Setting Up and Maintenance of Tissue and Cell Cultures, Elsevier Scientific Publishers Ireland, Ltd., (1985) pp. C109/1-C109/28. Lazar et al. (1987) Dev. Biol. Stand. 96: 315-323 (Abstract) reports a serum-free medium for the culture of Aedes aegypti cells that contains bovine serum albumin.
The fruit fly Drosophila melanogaster has for many years been the subject of intensive genetic analysis and various media have been developed for the culture of Drosophila cells. Inlow et al. (1989) J. Tissue Culture Methods 12: 13-16 discloses a serum-free medium for culture of Drosophila cells that contains yeast hydrolysate and a lipid emulsion. For media containing serum, see Shields et al. (1975) J. Embryol. exp. Morph. 33: 159-175; Lengyel et al. "Methods with Insect Cells in Suspension Culture II. Drosophila melanogaster" in Methods in Cell Biol. volume 10, pp. 195-208, (1975); Shields and Sang (1977) Drosophila Information Service, volume 52, page 161; Cross and Sang (1978) J. Embryol. exp. Morph. 45: 161-172; Sang (1981) "Drosophila Cells and Cell Lines" in Advances in Cell Culture volume 1, pp 125-182; and Ueda and Miyake (1987) In Vitro Cellular & Developmental Biology 23: 707-711.
There have been a few reports of serum-free media containing dextran or .beta.-cyclodextrin, however, the reported media are for the culture of mammalian cells. Pietrzkowski et al (1988) Folia Histochemica et Cytobiologica 26: 123-132 report a serum-free medium for the culture of chick embryo cell containing dextran. Pietrzkowski and Korohoda (1988) Folia Histochemica et Cytobiologica 26: 143-154 report a serum-free medium containing dextran for the culture of chick embryo fibroblasts. Ohmori (1988) Journal of Immunological Methods 112: 227-233 reports a serum-free medium which is able to support primary antibody responses by cultured murine lymphocytes. This medium is based on a basal medium supplemented with .beta.-cyclodextrin, insulin, transferrin, albumin, low density lipoprotein, putrescine and alanine.
A serum-free medium for large-scale culture of insect (Spodoptera frugiperda) cells was reported in Maiorella et al., (1988) Biotechnology 6: 1406-1410. In addition to a basal medium, the medium contained yeast extract, cod liver oil polyunsaturated fatty acid methyl esters, cholesterol and Tween. Murhammer and Goochee (1988) Biotechnology 6: 1411-1418 discloses a medium for the culture of Spodoptera frugiperda that contains serum.
It is an object of the invention to provide serum-free media for the culture of insect cells. It is also object of the invention to provide serum-free media for the culture of insect cells transformed to produce recombinant products that increase product yield. It is yet another object of the invention to provide serum-free media for the culture of Drosophila cells.